This invention relates to a device for eliminating impure ions in chromium plating bath and more particularly to a device for eliminating impure ions such as those of Fe, Ni, Pb, Cu, Zn which are ionized in the chromium plating bath and deteriorate the efficiency of plating, in the form of slime which precipitates on anode/s.
This invention also relates to an anode used in conjunction with the above-mentioned device.
This invention further relates to a chromium electroplating system combined with the above-mentioned device.
The chromium plating bath in the following description refers to chromium electroplating bath inclusive of ordinary chromium plating and hard chromium plating and a Chromate bath. The following description is generally made taking examples of the former chromium plating bath.
As for the chromium plating bath, usually so-called closed system is adopted, in which the plating bath is recirculated continuously to be regenerated since chromic acid is of rather higher cost. A well-known closed system is electric chromium plating is such that wasted water in a water-washing tank is condensed in a vacuum heator condensor and the condensed liquid content is fed back to the plating bath through a reservoir tank when the chromic acid content comes nearly to that of the plating bath, while evaporated water content in the condensor is condensed to water and again returned to the water-washing tank. This system is economical in that the chromium plating bath can be recirculated to be used in a long period of time and also Cr.sup.6.sup.+ is not discharged outside whereby it is free from pollution problem.
But a serious problem which resides in the abovementioned plant is that by the chromium electroplating operation over a long period of time, foreign metal ions such as those of Fe, Ni, Pb, Cu, Zn (hereinafter referred to as impure ions) which are ionized from the article to be plated to the bath in the course of plating operation come to increase to deteriorate the efficiency of plating so that better chromium electrode position is not expected after a long period whereby the used bath is subject to be discharged outside as waste liquid.
A countermeasures taken today for eliminating such impure ions is to provide so-called Diaphragm electrolysis device in which an unglazed pottery cylinder or an porous resin cylinder of tetrafluoroethylene is partitioned in the plating tank in the cylinder of which water solution of chromic acid exclusive of H.sub.2 SO.sub.4 is disposed and a cathode is immersed in the solution while on the anode side is disposed ordinal chromium plating bath inclusive of H.sub.2 SO.sub.4 thereby to make the above-mentioned impure ions precipitated on the cathode side during electrolysing. However, this device entails such disadvantages as not only troublesome operation and hard administration of operation but also higher material cost since chromic acid liquid is used inside of the cylinder as an operation liquid separated from the plating bath per se.